I removed my cat being that it was shot and reduced gas mileage. I own a 77 Monte Carlo and what I was told by an inspection shop was if the Monte came factory with a cat it will not pass inspection if it doesn't have one. The 77 Monte sounds like a monster with no cat or muffler in all seriousness. I thought it was a head turner before, but now it's insane. I need to know if these Monte's came with cats so I can keep this. Straight piping my 305 also improved gas mileage while improving sound.

 

I am sure it did. Cats I think came about in 1974 as my 74 Gp had one. We dont have inspection here in Indiana. They wont remove it without replacing it but if you take it off yourself and then go to a muffler shop, all is cool.

 

75 is the first year for the cat. i wouldnt run it straight piped if i were you. unless the car was making a monstrous amount of power, and even then there are mufflers for that kind of application. ive run open headers in my 80 with a built motor and it sounded like total **** not mention shook my eyeballs to death, and made it impossible to carry on a conversation. perhaps these people arent looking at your car going "damn that sounds awesome" maybe theyre saying"that fool has a huge hole in his exhaust." i can tell you that i have never run cats on my 80, but have always run headers, and mufflers. you do need a cat to pass a visual inspection. you have a couple of options though. take the cats you have and hollow them out, and run the exhaust through them(dummy cats). you could do what i did and just buy a sticker. its a little annoying every 2 years ponying up a 150 bucks, but it is what it is. another option is you can get classic insurance, and qq tags. that way you dont have to inspect it and do whatever you want to the car. all seriousness though. ditch the cat run 2.5' duals and pick a quality muffler. itll sound better, the world wont stare at you in awe of your stupidity, and your neighbors will thank you.